Homeostasis 1: What is Homeostasis? Structures and Processes of the Nervous System What is Homeostasis? Structures and Processes of the Nervous System

Homeostasis  Your body is always working to maintain your internal temperature near a set point of 37°C, blood glucose level at 100mg/mL and blood pH of 7.4.  The tendency of your body to remain around the same conditions is called homeostasis  Your body is always working to maintain your internal temperature near a set point of 37°C, blood glucose level at 100mg/mL and blood pH of 7.4.  The tendency of your body to remain around the same conditions is called homeostasis

Feedback Systems  Changes in the external environment or within your body can disturb homeostasis, so body systems are constantly monitoring changes.  Feedback systems consist of 3 parts:  A sensor, that detects the change and sends a signal to a control centre  A control centre, receives information and sends signals to the effectors when needed  An effector, that receives signals form the control centre and responds, resulting in a change to an internal variable.  The body has two different types of feedback systems to regulate its internal environment: negative and positive feedback systems.  Changes in the external environment or within your body can disturb homeostasis, so body systems are constantly monitoring changes.  Feedback systems consist of 3 parts:  A sensor, that detects the change and sends a signal to a control centre  A control centre, receives information and sends signals to the effectors when needed  An effector, that receives signals form the control centre and responds, resulting in a change to an internal variable.  The body has two different types of feedback systems to regulate its internal environment: negative and positive feedback systems.

Negative Feedback  Body works to reverse whatever change is detected in the body, and is brought back within normal range (set point).  i.e. body temperature:  You start to work out, your muscles gets warmer  Your body senses that you are warmer, and signals the control centre, which sends a signal to your sweat glands and to the blood vessels  Your sweat glands release sweat, blood vessels dilate. This continues until you return to the optimal temperature.  The opposite is true with cold and shivering.  Body works to reverse whatever change is detected in the body, and is brought back within normal range (set point).  i.e. body temperature:  You start to work out, your muscles gets warmer  Your body senses that you are warmer, and signals the control centre, which sends a signal to your sweat glands and to the blood vessels  Your sweat glands release sweat, blood vessels dilate. This continues until you return to the optimal temperature.  The opposite is true with cold and shivering.

Positive feedback  Positive feedback is when the body wants to increase or strengthen the change.  I.e. blood clotting: when you have a cut, you release platelets, those will stimulate more platelets to be released in the area until bleeding stops.  I.e. childbirth: uterus contracts, signals brain to release oxytocin (hormone that causes the uterine walls to contract more) from the pituitary gland, uterus contracts, and keeps going on this cycle until birth occurs.  Positive feedback is when the body wants to increase or strengthen the change.  I.e. blood clotting: when you have a cut, you release platelets, those will stimulate more platelets to be released in the area until bleeding stops.  I.e. childbirth: uterus contracts, signals brain to release oxytocin (hormone that causes the uterine walls to contract more) from the pituitary gland, uterus contracts, and keeps going on this cycle until birth occurs.

The Nervous System

Cells of the Nervous System  Composed of only 2 main types: neurons and glial cells.  Neurons are specialized to receive and conduct chemical stimuli. Neuron cells are organized into tissues called nerves.  Glial cells nourish the neurons, remove wastes and defend against infections. They also provide a supporting framework for the nervous system tissue.  Composed of only 2 main types: neurons and glial cells.  Neurons are specialized to receive and conduct chemical stimuli. Neuron cells are organized into tissues called nerves.  Glial cells nourish the neurons, remove wastes and defend against infections. They also provide a supporting framework for the nervous system tissue.

Structure of a Neuron  Dendrites: are short, branching terminals that receive nerve impulses from other neurons or sensory receptors and relay the impulse into the cell body.  Cell Body: has the nucleus and is the site of the metabolic reactions, process input form dendrites.  The axon: conducts impulses away from the cell body. The terminal end branches into many fibres and releases chemicals into the space between it and the receptors or dendrites of neighbouring cells.  Myelin Sheath: a fatty, insulating glial layer that encloses some of the neurons. It is there for protection and speeds the rate of nerve impulse transmission.  Dendrites: are short, branching terminals that receive nerve impulses from other neurons or sensory receptors and relay the impulse into the cell body.  Cell Body: has the nucleus and is the site of the metabolic reactions, process input form dendrites.  The axon: conducts impulses away from the cell body. The terminal end branches into many fibres and releases chemicals into the space between it and the receptors or dendrites of neighbouring cells.  Myelin Sheath: a fatty, insulating glial layer that encloses some of the neurons. It is there for protection and speeds the rate of nerve impulse transmission.

Neuron

3 Types of Neurons  Functionally, neurons are classified into:  Sensory input: sensory receptors (like in the skin) receive stimuli and form a nerve impulse that is sent to the central nervous system.  Integration: interneurons are found in the CNS that act as a link between sensory and motor neurons. They process incoming sensory information and relay outgoing motor information.  Motor Output: motor neurons transmit information form the CNS to the effectors (muscles, glands, organs) that respond to impulses from the motor neurons.  Functionally, neurons are classified into:  Sensory input: sensory receptors (like in the skin) receive stimuli and form a nerve impulse that is sent to the central nervous system.  Integration: interneurons are found in the CNS that act as a link between sensory and motor neurons. They process incoming sensory information and relay outgoing motor information.  Motor Output: motor neurons transmit information form the CNS to the effectors (muscles, glands, organs) that respond to impulses from the motor neurons.

Reflex Arc  Some neurons are organized so that they allow your body to react very quickly in times of danger even before you are aware of the threat consciously.  Called reflexes  Examples: moving hand from hot objects, blinking when something moves towards your eye.  Usually use only 3 neurons to transmit messages  Some neurons are organized so that they allow your body to react very quickly in times of danger even before you are aware of the threat consciously.  Called reflexes  Examples: moving hand from hot objects, blinking when something moves towards your eye.  Usually use only 3 neurons to transmit messages

Practice:  Try the Inquiry Investigation on page 374  P.348 # 5, 8, 9, 10.  P.354 # 7, 9, 10  Try the Inquiry Investigation on page 374  P.348 # 5, 8, 9, 10.  P.354 # 7, 9, 10